1. Field of the Invention
The present invention relates to an indexable cutting insert which may be attached to various kinds of insert cutters.
2. Prior Art
FIGS. 19 to 21 depict an end mill which utilizes a conventional, indexable cutting insert. The end mill comprises a cylindrical tool body 1 having an axis of rotation O therethrough and having an axially forward end portion 2 of a reduced diameter. A chip pocket 3 is formed in the forward end portion 2 in such a manner that the thickness of the portion 2 increases gradually in an axially rearward direction of the tool body 1. An insert-receiving recess 5 is formed in the foremost corner of the bottom 4 of the chip pocket 3 which is facing in a direction of rotation of the tool body 1, and an indexable cutting insert 7 is received in the insert receiving recess 5 and secured thereto by means of a clamp screw 6.
The insert 7 is of a positive type and has generally parallelogrammic front and rear faces 9 and 10 disposed parallel to each other, the front face 9 serving as a rake surface while the rear face 10 serves as a seating surface to be held in contact with a bottom 19 of the insert receiving recess 5. A diagonally opposite pair of acute corners of the front face 9 are formed into nose portions 11 and 11, respectively. Furthermore, each pair of marginal ridges of the front face 9, which are disposed so as to sandwich a respective nose portion 11 therebetween, define a peripheral cutting edge 16 and an end cutting edge 17, respectively. In addition, the insert body 8 has a central mounting aperture 18 formed therethrough.
Moreover, the insert receiving recess 5, to which the above insert 7 is secured, is shaped in conformity with the insert body 8 such that the cutting edges 16, 17 and 11 protrude from the tool body 1 and can be indexed in active cutting positions. Furthermore, the bottom 19 of the insert receiving recess 5 is flat and is inclined with respect to the axis O of the tool body 1 in such a manner that the thickness H of the forward end portion 2 increases gradually in an axially rearward direction of the tool body 1.
In the end mill as described above, the insert 7 undergoes a large cutting load when brought into engagement with a workpiece to cut it, and hence it is preferable that a sufficient rigidity is imparted to the forward end portion 2 of the tool body 1. For this reason, the chip pocket 3 is formed in such a manner that the thickness of the forward end portion 2 increases gradually in an axially rearward direction of the tool body 1, and the bottom 19 of the insert receiving recess 5 is formed in such a manner that it is inclined with respect to the axis O of the tool body 1, and that the thickness H of the forward end portion 2 of the tool body 1 increases gradually in an axially rearward direction of the tool body 1.
However, when the insert 7, in which the rake surface and the seating surface are formed parallel to each other, is secured to the insert receiving recess 5, the rake surface of the insert 7 will also become inclined with respect to the axis O of the tool body 1. Therefore, when an angle defined between the bottom 19 of the insert receiving recess 5 and the axis O of the tool body 1 is set to a prescribed value .theta., the axial rake angle .gamma..sub.a1 for the insert 7 comes to have the same absolute value .theta., but becomes negative, and consequently, deterioration of the cutting performance cannot be avoided.
Furthermore, the radial rake angle .gamma..sub.r1 of the insert 7 is determined by the thickness H of the forward end portion 2 of the tool body 1 and the thickness of the insert 7. However, in order to impart a sufficient rigidity to the forward end portion 2 of the tool body 1, its thickness H cannot be reduced. In addition, the thickness of the insert 7 cannot be reduced either in consideration of its rigidity or strength. As a result, the radial rake angle .gamma..sub.r1 becomes unduly large in a negative direction, and the cutting performance is thereby further deteriorated.